Gas-tight alkaline accumulator with valve assembly

ABSTRACT

In a gas-tight alkaline accumulator with a casing which at least partially comprises plastic material and in which are arranged electrodes which are surrounded by an electrolyte and which are respectively separated from each other by a separator, wherein the electrodes are connected to pole contacts for electric current to be fed to and away therefrom, in order to increase the operating reliability of the accumulator and to avoid further disadvantages, there is provided a valve having an opening which passes through the casing of the accumulator, and a deformable element which, in the event of an increased pressure occurring within the casing, provides for liberation of the opening and, after a drop in the increased pressure, closing of the opening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a gas-tight alkaline accumulator.

2. Discussion of Prior Art

The requirements made in respect of accumulators of that kind areprogressively rising, in the field of electronics. Continuouslyincreasing mobility and rising demands in regard to operating comfortare compelling the development of ever more powerful, lighter andsmaller energy sources. Thus for example hand-held mobile telephonessuch as the present-day D-network or future E-network telephones areadmittedly becoming smaller and smaller and lighter and lighter, but, inorder to be able to achieve market successes at all, they must ensureminimum times in respect of operational readiness, which are usually inthe range of several hours.

In regard to the development of integrated circuits and very large-scaleintegrated chip sets for mobile telephones of that kind or otherportable equipment such as for example lap-tops or palm-tops (portablecomputers), camcorders and hearing aids, enormous sums are spent onminiaturising the electronic circuit assemblies, but corresponding smallenergy sources are also required.

With the development of prismatic casings of plastics material forgas-tight alkaline accumulators, it has already been possible to achieveconsiderable success in terms of improving those accumulator properties.The use of a light plastic material casing and adaptation of the casingto the geometries which are predetermined by the respective equipmentmanufacturer or adaptation to wide-spread rectangular casingconfigurations provide for light accumulators with a high storagedensity. With adapted electrode shapes, it is possible to use almost theentire remaining volume of the equipment for the storage of electricalcharge; reference is directed in this respect to German patentapplication No P 43 25 464, the disclosed content of which is completelyincorporated herein by reference thereto and made the content of thepresent application.

However, it is precisely in the case of light and small accumulatorsthat a high degree of attention must be paid to the prevention ofbursting, in order to avoid unnecessarily losing the advantagesattained, by virtue of an additional thickness of material or a moreexpensive casing structure. In the event of overcharging or chargingwith excessively high currents, and also after polarity reversal or ashort-circuit, high increased pressures may occur in the interior of thecasing, and such pressures can ultimately result in bursting of suchcells.

Although glass or carbon fibre-reinforced plastic materials have highlevels of strength and impact toughness, bursting of the accumulatormust be certain to be excluded at any time. Particularly in the case ofhand-held items of equipment, the explosive escape of the stronglyalkaline and corrosive electrolyte can result in injury to personsand/or damage to expensive items of equipment.

In the case of larger accumulators, to control the increased pressuresand the safety risks involved therewith, use is made of screw-inpressure-relief valves which however cannot be used in the case of smallgas-tight alkaline accumulators, because of the additional amount ofspace required for the screwthread and the valve unit which is generallyof an expensive construction.

The desired-rupture locations which are known in the field of gas-tightalkaline accumulators with a metal casing are also disadvantageous inregard to damage to high-quality equipment in the event of continuingdischarge of the electrolyte. After the desired-rupture location hasopened, it continues to result in a loss of sealing integrity of theaccumulator casing, and that can therefore involve the undesireddischarge of further electrolyte.

SUMMARY OF THE INVENTION

Tests have further shown that such desired-rupture locations used inconnection with metal casings cannot be directly transferred to plasticcasings. Metal casings, in particular of round cells, can in partwithstand pressures of 20 bars and higher, but, at increased pressuresof such a high magnitude, prismatic and in particular rectangularplastic casings may suffer from bulging effects which disturb theirdimensional accuracy and which are therefore to be avoided.

The concepts developed in connection with lead-acid accumulators alsogenerally cannot be applied to small alkaline gas-tight accumulatorswith a high power density. Lead-acid accumulators generally havesubstantially more space, and neither the weight nor the form ofadditional valves play an essential part.

EP-A1-0 049 081 discloses an electrochemical cell with a valve arrangedin the pole contact. By virtue of the valve being arranged in the polecontact, it is possible that the volume required for the valve is notoccupied within the cell, so that the loss in volume which reduces thestorage capacity can be avoided. A disadvantage with that arrangementhowever is that the escape of electrolyte which is caused by anincreased pressure can contaminate the pole contacts and consequentlyeven damage then.

EP-A1-0 306 146 discloses a valve structural group which is lessdesigned for reducing an increased pressure, but which is ratherintended for venting a battery chamber. The cylindrical valve elementsshown therein surround the valve seat in a curtain-like fashion withonly a light contact pressure. Although in that way it is possible toproduce high flow volumes by virtue of the sealing element being setback to afford a large space, the sealing capability is inadequate athigh pressures as occur for example in gas-tight alkaline accumulators.Because of the small gas volumes remaining, the escape of very smallamounts is generally sufficient in alkaline accumulators, to provide fora considerable reduction in pressure.

The object of the present invention is therefore that of increasing theoperational reliability and safety of an accumulator and at the sametime eliminating or at least alleviating the above-discusseddisadvantages.

That problem is solved by an accumulator having a casing which at leastpartially is made of plastic material and in which are arrangedelectrodes, an electrode separator, and electrolyte surrounding theelectrodes. Pole contacts are connected to the electrodes for feedingelectric current to and away from the electrodes. A valve for reducingincreased pressure occurring in said accumulator has an opening thatleads through the casing and a deformable element arranged to provideliberation of the opening in the event an increased pressure occurswithin the casing and for closing the opening after the increasedpressure falls. A predeterminable increased pressure for opening thevalve is produced by a defined upsetting of the deformable element.

In the event of an increased pressure occurring in the cell, thedeformable element provides for opening and immediate re-closing afterthe increased pressure has been reduced so that gas is discharged onlyfor a short period of time and only very small amounts of gas orentrained electrolyte constituents are discharged. In that way thecapacity of the accumulator is adversely affected only to a slightdegree, even if at all.

If, by virtue of its own elasticity, the deformable element bears inforcible sealing contact against the opening of the accumulator casing,both liberation of the opening in the event of an increased pressure andalso the sealing effect in the normal operating condition are achievedby virtue of a single elastic deformable element. The two functionsrequire only one component, so that the valve assembly is simple toproduce, while occupying a small amount of space. Losses of volumeremain low, and a suitable arrangement of the valve assembly, which isdescribed in greater detail hereinafter, can avoid losses of capacity.

If the deformable element is supported at the side which is opposite tothe opening, and if therefore it is subjected to a defined upsettingeffect, a predeterminable increased pressure value can be produced, foropening the valve. With the modulus of elasticity being known, theupsetting effect of the deformable element, together with the known areaof the opening within the accumulator casing, can be easily calculated,taking the predetermined increased pressure value as the basic startingpoint. In addition various values in respect of the increased pressurecan be easily achieved, for example for different accumulator designs,merely by virtue of the selection of the length of the deformableelement.

In the case of rectangular accumulators in the range of sizes of about17 mm×6 mm×48 mm, it was possible for the increased pressure, as fromwhich the valve opened, to be easily reproducibly adjusted at between2.5 and 10 bars. It is however also possible to achieve any otherincreased pressure values. An increased pressure of 3.5 bars or 4.5 barswas found to be desirable in regard to avoiding the above-describeddisadvantages.

If there is arranged adjacent the deformable element a discharge passagewhich extends within a wall beside the deformable element, thatarrangement, in spite of the small size of the discharge passage,already affords a labyrinth arrangement for escaping gases and forentrained constituents of the electrolyte. The reduction in pressuretakes place in a more regular manner as the discharge passage, with itscross-section, produces the defined gas discharge effect, anddischarging gas components are already decelerated within the dischargepassage. Forming the discharge passage within a wall of the chamber ofthe deformable element is both possible in an inexpensive fashionwithout involving further structural groups, and simple from the pointof view of the production procedure involved.

If the deformable element is arranged with lateral play or clearancewithin a valve chamber, the clearance between the sealing element andthe chamber accommodating it results in a space with a pre-chambereffect, in which case the increased pressure is already relieved withinthat chamber, and the discharge of gas occurs at a substantially lowerpressure, relative to the exterior of the accumulator.

With a retaining element which can be pressed in from the outside, thevalve assembly can be produced independently of the remainingaccumulator assemblies. When accumulators are otherwise assembled, thedeformable element can be subsequently fitted into the valve chamber andthe retaining element can be pressed on from the outside. In that way itis possible to use the same accumulators for different increasedpressures, which simplifies stockkeeping, and it is also possible todesign the accumulators with deformable elements of different lengths,depending on the respective use involved.

If, in an alternative embodiment, the deformable element has acup-shaped cover cap fitting laterally thereover, and is held in contactbearing against same at its rear side, with the cover cap having a valvedischarge opening, that makes it possible to construct a mechanicallystable valve assembly of very small dimensions, which is shielded fromexternal influences. The casing is further mechanically strengthened byvirtue of the cover cap being welded to the casing, preferably bythermal welding or by ultrasound welding. The additional valve dischargeopening in the cover cap enhances the pre-chamber effect and can furtherreduce the speed of the issuing gases.

If, in a further alternative embodiment, the deformable element is heldby a cup-shaped cover cap in bearing contact at the front side thereof,and if in that arrangement the opening in the casing is disposed in theend portion of the cup-shaped cover cap, the valve assembly can only beseen through the discharge opening from the exterior, protected frommechanical influences.

A lateral edge of the cover cap which is of a wider configuration in theouter end region improves the mechanical contact between the cover capand the casing as the welding effect is improved by larger wall regionswhich bear against each other. In addition the creep distance for thedischarge of gases or electrolyte is increased in length and the sealingproperties are improved.

Arranging the valve in the cover of the accumulator makes it possiblefor the valve assembly to be produced simultaneously with the cover. Ifthe valve is arranged between the pole contacts of the accumulator, thatinvolves a location which is mechanically protected from externalinfluences, and it is possible to use the space between the electrodefeed lines, within the accumulator, without losses in capacity.Furthermore the valve body can serve as mechanical centering and/orholding means for the electrode assembly and can secure the positionthereof mechanically within the accumulator.

An embodiment which is highly advantageous from the point of view ofproduction procedure involves the hot-in-hot injection welding of a partof the plastic casing with the deformable element. In the hot-in-hotinjection welding procedure used, the welded surface forms amechanically strong hold upon injection of the plastic material of thedeformable element along the contact surface, relative to the plastic ofthe accumulator casing. Preferably then both the at least one part ofthe casing and also the deformable element comprise a thermoplasticelastomer, in particular a modified polyamide, astyrene-ethylenebutylene-styrene copolymer, and/or a polypropylene. Thehard plastic material is so adjusted in respect of its hardness, forexample by the addition of plasticisers and/or by the selection of itsdegree of cross-linking, that it achieves the usual levels of casingstrength.

The hardness of the softer plastic material of the deformable elementcan be so adjusted by the addition of plasticisers and/or by theselection of its degree of cross-linking that it is in the range ofknown sealing materials.

In a particularly advantageous manner, the deformable element may behot-in-hot injected simultaneously with the seals of the accumulatorcasing or simultaneously with the cover seals and/or the pole contactseals.

DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter by means ofvarious embodiments and with reference to the accompanying drawings inwhich:

FIG. 1 is a view in section in the longitudinal direction through anaccumulator in accordance with a first embodiment according to theinvention,

FIG. 2 is a view on an enlarged scale of a part of the valve assembly ofthe accumulator shown in FIG. 1 without the retaining element andwithout the deformable element,

FIG. 3 is a view of the cover assembly of the accumulator from FIGS. 1and 2 after injection welding of the seals from the inside of theaccumulator,

FIG. 4 is a view of the cover assembly of the accumulator from FIGS. 1through 3 after the injection welding of the seals, from the front,

FIG. 5 is a view in cross-section taken along line A--A in FIG. 4through the cover assembly,

FIG. 6 is a view of the way in which the valve assembly according to theinvention in the first embodiment is fitted together,

FIG. 7 is a view in cross-section through a valve assembly of a secondembodiment according to the invention,

FIG. 8 is a view in cross-section through a valve assembly of a secondembodiment according to the invention, but in a direction turned through90° relative to the cross-section shown in FIG. 7,

FIG. 9 is a view of the valve assembly shown in FIGS. 7 and 8, from theoutside,

FIG. 10 is a view in cross-section through a third valve assemblyaccording to the invention, in a third embodiment, and

FIG. 11 is a view of the valve assembly shown in FIG. 10 from theoutside.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The gas-tight alkaline accumulator shown in FIG. 1, in accordance with afirst embodiment of the invention, is generally identified by referencenumeral 1 and includes a casing 2 at least partially comprising plasticmaterial, with a cover 3. Arranged within the casing 2 are positiveelectrodes 5 and negative electrodes 6 which are surrounded by anelectrolyte and which are separated from each other by a separator 4.The electrodes 5 and 6 are respectively connected to a positive polecontact and a negative pole contact 8 for electric current to be fed toand away therefrom.

A valve 9 is arranged between the pole contacts 7, 8 in the cover 3 andincludes an opening 10 which passes through the casing 2, in particularthrough the cover 3, of the accumulator 1. A deformable element 11 isheld in a valve chamber 13, in a condition of bearing sealingly againstthe opening 10, being upset by a retaining element 12. When increasedpressure occurs within the casing 2, the pressure which bears againstthe cross-sectional area of the opening 10, as from a predeterminableincreased pressure value, causes the deformable element 11 to move backand in that way causes at least partial liberation of the opening 10,whereby gas is discharged and the increased pressure within the casing 2is reduced. After the increased pressure has been reduced, thedeformable element 11 comes into sealing contact with the opening 10,subsequently thereto again, and that causes the discharge of gas to beterminated.

By the choice of suitable materials such as for example rubber or thethermoplastic materials which are described in greater detailhereinafter, the deformable element can be caused to bear forcibly insealing contact against the opening 10 by virtue of its own elasticity,without further spring elements.

When the valve assembly is fitted together, as is illustrated in FIG. 6,the retaining element 12 provides for a defined upsetting effect for thedeformable element 11, and that upsetting effect can be used to adjust apredetermined increased pressure. The retaining element 12 compriseschemically inert material, in particular the same material as the casing2. With the modulus of elasticity of the material of the deformableelement 11 being known, it is possible to calculate the necessary forcefor the sealing contact of the deformable element 11 and thus thenecessary upsetting effect in respect thereof, from the cross-sectionalarea of the opening 10 and the predetermined increased pressure foropening same. The increased pressure as form which the valve opens isbetween 2.5 and 10 bars, preferably being 3.5 or 4.5 bars.

Arranged adjacent the deformable element 11 is a discharge passage 14which extends within a wall 15 in the valve chamber 13 beside thedeformable element 11 from the opening 10 to the exterior of theaccumulator 1 or as far as the elastic arms 16, 17.

The retaining element 12 which is only diagrammatically illustrated inFIG. 2 is securely held by an elastic positively locking connectionbetween the two elastic arms 16, 17 of the casing 2, which adjoin thevalve chamber 13 in the longitudinal direction. The deformable element11 is gripped between the retaining element 12 and the opening 10 insuch a way that there remains a lateral play or clearance within thevalve chamber 12, even after upsetting of the deformable element 11.

FIGS. 3 and 4 are a view on to the cover assembly from the front sideand the rear side, of the valve 9 arranged in the cover 3. Also showntherein are the seals 18, 19 of the pole contacts 7, 8 and the seal 20for sealing off the cover 3. The seals 18, 19 and 20 are each joined tothe cover by hot-in-hot injection welding.

The seal 20 for the cover 3, as shown in FIG. 5, is arranged in such away that projecting lateral portions 21 of the cover 3 permit securewelding thereof to the remaining part of the casing 2.

FIGS. 7, 8 and 9 show a second embodiment of the valve 9 according tothe invention.

It is pointed out that, in all embodiments, the same components orcomponents with the same action are denoted by the same references.

In this embodiment the deformable element 11 is arranged in a valvechamber 13 formed by a portion of the casing 2, in particular the cover3, and a cover cap 22. The cover cap 22 laterally engages over thedeformable element 11 and bears against the rear side thereof in such away as to produce the above-described defined upsetting effect. Thedischarge passage 14 arranged in the wall 15 has a valve dischargeopening 23 to the outside of the accumulator 1. In the radial direction,the cover cap has a lateral edge 24 which is wider in the outer endregion and which is positively lockingly fitted into the casing 2, inparticular the cover 3. In the region of the lateral edge 24 the covercap 22 is connected to the casing 2, in particular the cover 3, bythermal welding or ultrasound welding.

As shown in FIG. 1, the valve 9 in the second embodiment and also thethird embodiment described hereinafter can be arranged in the cover 3between the pole contacts 7 and 8.

In an alternative configuration however the valve 9 of the second andthird embodiments can be arranged at any other location, such as forexample in the bottom 25 of the accumulator 1.

The third embodiment according to the invention has a cover cap 22 inwhich the opening 10 is provided as in the preceding embodiment. Thedischarge opening 23 is provided in the casing 2, in particular in thecover 3. The cover cap 22 bears against the front side of the deformableelement 11.

The deformable element 11 is produced by hot-in-hot injection weldingtogether with the casing 2, in particular the cover 3. For that purposea passage 26 connects the seals 18, 19 of the pole contacts 7, 8 to anopening 27 which permits the passage therethrough of the hot-injectedplastic material, for producing the deformable element 11.

Depending on the respective arrangement of the valve 9, preferably theseals 18, 19 for the pole contacts 7, 8 and/or the seal 20 for the cover3 are also formed in production of the deformable element 11.

Although the deformable element 11 can comprise any chemicallyresistance elastic material, when using the hot-in-hot injection weldingprocedure, thermoplastic elastomers, in particular modified polyamide,styrene-ethylene-butylene-styrene copolymer and/or polypropylene arepreferred for that purpose. The plastic material of the deformableelement is adjusted in terms of its hardness in such a way that it is inthe range of known sealing materials, by virtue of the addition ofplasticisers and/or by the selection of the degree of cross-linkingthereof. The hardness of the plastic material of the casing 2 and inparticular the cover 3 is so adjusted that it reaches the usual levelsof casing strength.

In a further configuration, to improve the strength properties, glass,carbon, a carbon-reinforced plastic material, such as KEVLAR or boronfibre material is added embedded in the plastic material of the-casing2, in particular the cover 3.

I claim:
 1. A gas-tight alkaline accumulator comprising:a casing comprised at least partially of plastic material, electrodes arranged in said casing, a separator separating said electrodes, an electrolyte surrounding said electrodes, pole contacts connected to said electrodes for feeding electric current to and away from said electrodes, a valve (9) for reducing increased pressure occurring in said accumulator, said valve having an opening (10) leading through said casing (2, 3), and a deformable element (11) arranged to provide liberation of said opening (10) in the event an increased pressure occurs within said casing (2, 3) and for closing said opening (10) after said increased pressure falls, such that a predeterminable increased pressure for opening said valve (9) is produced by a defined upsetting of said deformable element (11).
 2. The accumulator according to claim 1, wherein said deformable element (11) is arranged to bear forcibly and sealingly against said opening (10) by virtue of elasticity of said deformable element (11).
 3. The accumulator according to claim 1, wherein said deformable element (11) is arranged to be supported opposite to said opening (10).
 4. The accumulator according to claim 1, wherein said increased pressure that opens said opening (10) is between 2.5 and 10 bars.
 5. The accumulator according to claim 4, wherein said increased pressure is 3.5 bars.
 6. The accumulator according to claim 1, further comprising a discharge passage (14) arranged adjacent said deformable element (11), which discharge passage (14) extends within a wall (15) arranged beside said deformable element (11).
 7. The accumulator according to claim 1, further comprising a valve chamber (13) within which said deformable element (11) is arranged with lateral clearance, and a retaining element (12) for holding said deformable element (11) at a rear side of said deformable element (11) within said valve chamber (13).
 8. The accumulator according to claim 1, further comprising a cup-shaped cover cap (22) engaging laterally with said deformable element (11) and contacting and bearing against said deformable element (11) on a rear side of said deformable element (11), said cover cap (22) having a valve discharge opening (23).
 9. The accumulator according to claim 1, further comprising a cup-shaped cover cap (22) engaging laterally with said deformable element (11) and contacting and bearing against said deformable element (11) on a rear side of said deformable element (11), said cover cap having an end portion in which said opening (10) is arranged, said casing (2, 3) having a valve discharge opening (23).
 10. The accumulator according to claim 8, wherein said cover cap (22) has a lateral edge (24) that is wider in an outer end region.
 11. The accumulator according to claim 1, wherein said valve (9) is arranged in a cover (3) of said accumulator.
 12. The accumulator according to claim 1, wherein said valve (9) is arranged between said pole contacts (7, 8).
 13. The accumulator according to claim 1, wherein said accumulator (1) comprises a prismatic accumulator.
 14. The accumulator according to claim 13, wherein said accumulator (1) comprises a rectangular accumulator.
 15. The accumulator according to claim 1, wherein said deformable element has been hot-in-hot injection welded at least into a part of said casing (2, 3).
 16. The accumulator according to claim 15, wherein said deformable element (11) has been hot-in-hot injection welded simultaneously with seals (18, 19, 20) of said casing (2, 3).
 17. The accumulator according to claim 15, wherein said deformable element (11) has been hot-in-hot injection welded simultaneously with a cover seal (20).
 18. The accumulator according to claim 15, wherein said deformable element (11) has been hot-in-hot injection welded simultaneously with pole contact seals (18, 19).
 19. The accumulator according to claim 1, wherein at least a part of said casing (2) and said deformable element (11) comprise a thermoplastic elastomer.
 20. The accumulator according to claim 19, wherein said thermoplastic elastomer is selected from the group consisting of modified polyamide, styrene-ethylene-butylenestyrene copolymer and polypropylene.
 21. The accumulator according to claim 19, wherein said casing (2) and said deformable element (11) are of different hardnesses.
 22. The accumulator according to claim 1, wherein said casing includes material selected from the group consisting of glass, carbon, carbon-reinforced plastic material, and boron fibers embedded in said plastic material. 